1. Field of the Invention
The present invention concerns an electric injection mechanism for driving a screw driver using an electric motor.
2. Detailed Description of the Prior Art
In existing systems, electric injection mechanisms having an electric motor such as a servomotor or the like as driving source, and injection-driving a screw by converting rotation movement by the electric motor into liner movement by a ball screw shaft and a ball nut member, have included examples adopting a single ball screw shaft and examples adopting a plurality of ball screw shafts.
In any of these existing types, a screw driver is inserted movably forward and backward into a guide bar between a pair of front and rear plates. The ball screw shaft (rotated by the electric motor) engages with the ball nut member installed in the screw driver. Further, in such existing systems, the rear end of a screw in an injection heading cylinder mounted at the front middle of a front plate is rotatably linked to the front middle of the screw driver.
In such configurations, if the injection heating cylinder and the screw driver are decentered even slightly in mounting, the injection heating cylinder and the screw therein are also decentered. This may provoke gnawing or breakage, and, moreover, the parallelism with respect to a guide bar supporting the screw driver is affected, increasing the sliding resistance against the movement of the screw driver. Such interactions may easily result in inconvenience of control or other troubles during operation.
The centers of the injection heating cylinder and screw driver are defined by the processing accuracy or the assembling accuracy of respective members making up the injection mechanism. It is extremely difficult to adjust misalignment after assembly is completed. However, as the misalignment often appears in the height direction as an effect of the load, and the misalignment during operation is caused by the inflection of the guide bar, due to the load of the screw driver, most of problems due to misalignment can be resolved, if the height of the screw driver can be adjusted by any means, even after assembly.
The present invention addresses the above problems, and has an object of providing a novel electric injection mechanism allowing adjustment of the height of the screw driver by an extremely simple means after assembly. The present invention allows the injection heating cylinder and the screw driver to be easily aligned, and prevents misalignment during operation.
According to the above described objects of the invention and others, the present invention includes a front plate provided with an injection heating cylinder having a screw inside at the front middle, a rear plate provided with an electric motor for injection-driving, an installation member affixing both plates, a plurality of guide bars installed between the plates, linking the pair of front and rear plates. The present invention further includes a screw driver moveable forward and backward between the plates by insertion into the guide bars, and a driving means including a ball screw shaft and ball nut member disposed over the screw driver and the rear plate by connection with the electric motor. A member for centering the injection heating cylinder and screw driver, slidably supporting the screw driver, and interposed between the installation member and the screw driver, and having a height adjustment mechanism, is installed at both sides of the lower portion of the screw driver.
In addition, the driving means includes a pair of ball screw shafts rotatably juxtaposed over the front plate and rear plate, and a pair of ball nut members at both sides of the screw driver, installed in the screw driver and engaging respectively with the ball screw shafts.
Further, the centering member includes a pair of overlapping wedge-shaped members, forming a contact surfaces respectively with their slanted surfaces, both linked relatively movably by an adjustment screw, with one affixed to the bottom face of the screw driver, while the other is put on the top face of the installation member.